Environment and heredity – the beginning

Alexandra Bruter, <url>Congenital or acquired?

To what extent is it innate, and to what extent is it acquired? Disputes of this kind are conducted about almost any property of the human body, and, especially zealously, about deviations from the norm.

About some diseases that have a simple genetic nature, it is usually safe to say that they are congenital. And about infectious diseases – that they are acquired. But it's not so simple here either. Phenylketonuria is a hereditary disease that occurs due to a mutation in the gene encoding the enzyme needed for the breakdown of the amino acid – phenylalanine. Accumulating phenylalanine and its incorrect toxic decomposition products cause damage to the central nervous system, the child lags behind in mental development. Phenylketonuria is often cited as a classic hereditary disease. It is noteworthy that the observance of a special diet in the first years of life, excluding phenylalanine, allows the child to develop normally. That is, from a genetic point of view, a person is sick, but in fact – healthy. So is it a congenital disease or an acquired one?

Two people came into contact with a flu patient. One got infected, the other didn't. Could it be that due to some innate genetic features, the immunity of one of them copes better with viruses?

There is a hereditary predisposition to many deadly diseases (cardiovascular, oncological). But here are two identical twins with such a predisposition. One is sick, and the other is healthy. What is the reason for this? With the fact that they led different lifestyles? Or with the fact that one was just more lucky? To date, we do not know the answer to this question. Scientists have learned to count correlations quite well, but correlations by themselves do not mean a causal relationship (all people who have eaten cucumbers have already died or will die in the next 150 years), and in order to detect a causal relationship, it is necessary to understand the mechanism. It is much more difficult to do this than to calculate the correlation coefficient.

The sibling (a common word for siblings) method is considered the gold standard for finding out what the hereditary component is in a particular trait. For the study, pairs of identical twins who grew up in the same family, siblings who are not twins, and siblings who grew up in the same family, of whom one or more were adopted, are selected. Sometimes it is possible to complete the picture by finding pairs of siblings (sometimes even twins) who grew up in different families. Based on how often the studied trait is simultaneously present or absent in pairs of different types, it is possible to draw conclusions about the role of heredity.

Scientists, and especially those who try to implement their ideas in everyday life, enter a minefield when it comes to innate and acquired behavioral traits. The results of such studies may conflict with two very important concepts for Western society: the concept of equal opportunities and the concept of free will.

For example, in an experiment during which the IQ of twins, ordinary siblings and siblings, among whom there were adopted, was evaluated, it turned out that the IQ of an adult depends on heredity more than on upbringing. In fact, the IQ correlation coefficient for homozygous twins who grew up separately was 0.76 (where 1 corresponds to an imminent coincidence, and 0 corresponds to the absence of a connection between events), and for people who grew up together who are not related to each other – 0.04. These results indicate a very high hereditary component of IQ. Approximately the same hereditary component of growth. The concept of equal opportunities suffers slightly from this, but not much: so far, no convincing evidence has been found of the influence of IQ on income.

The concept of free will risks to suffer more with time. It is commonly thought that our actions are dictated by our conscious decisions, and we are fully responsible for them. If it is possible to prove that actions can be caused by genetic variants, responsibility for them will be in question: well, in fact, it is not the person's fault that he got a variant of the gene associated with increased aggressiveness, he got it at all nine months before his birth, he did not choose it in any way. Arguments of this kind have already been put forward in American courts. Basically, they relate to two genetic conditions

The first is a chromosomal anomaly caused by the non–divergence of sex chromosomes during spermatogenesis. As a result, boys with genotype XYY are born. Such boys look quite ordinary, their abnormal genotype is usually detected by chance. They grow into fertile men slightly taller than average. Sometimes they may have developmental delays and reduced learning ability, but scientists have not been able to identify the connection of such a genotype with increased aggressiveness, although studies have been conducted.

The second condition, which apparently does have a correlation with greater aggressiveness, is called Brunner syndrome. The disease occurs due to a mutation in the gene encoding monoamine oxidase A (MAOA), an enzyme that destroys monoamines: adrenaline, norepinephrine, serotonin and dopamine. The mutation makes the enzyme inactive, and monoamines accumulate in the brain. Such people have noticeably reduced intelligence, they are prone to cruelty, violence and antisocial behavior.

The mutation that causes Brunner syndrome completely inactivates MAOA. At the same time, there are a number of polyformisms of the regulatory region of the corresponding gene, some of which are also associated with aggressive and antisocial behavior.

It would seem that this is exactly the case when heredity can be blamed for antisocial behavior. But it's too early to rejoice, it will not be possible to divide everyone into lambs and goats at birth yet. It turned out that in carriers of the variant associated with increased aggressiveness, the manifestations of such behavior in the future are closely related to cases of violence and other extreme forms of trouble in the family at an early age. Everything turns out almost as with phenylketonuria: there is a mutation, but whether it manifests itself depends on the living conditions in childhood.

In 2009, American lawyers managed to get their client to commute the death penalty to 32 years in prison, citing as an argument a combination of the unsuccessful version of the MAOA gene in the client and the fact that he was abused as a child.

The ending follows.

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06.07.2015